1. Field of the Invention
This invention pertains generally to a damping support spring for supporting an object and more particularly to a spring arrangement for supporting a cold finger of an open-cycle cryocooler.
2. Description of the Related Art
The development of very low phase noise in cryogenic radars requires the use of sapphire dielectric resonators at X-band frequencies operating at cryogenic temperatures to achieve loaded Q's greater than 3.times.10.sup.6. A phase-noise goal of -145 dB.sub.c /Hz at 1 KHz offset, which corresponds to an allowable frequency jitter .DELTA.f of 3.times.10.sup.-5 Hz, imposes significant vibration sensitivity requirements on the resonator. A dielectric resonator/oscillator including a sapphire puck that is soft-mounted in a metal enclosure operating in a 5.sup.th -order whispering gallery mode wherein the resonator frequency is affected by very small relative axial and radial displacements of the inner surfaces of the enclosure, so that a support spring must provide effective vibration isolation in all three directions to achieve a required low phase-noise goal. The support spring must be damped to avoid excessive vibration transmission at its natural frequencies and it must have high thermal conductivity to conduct heat from the resonator to the cold finger without excessive temperature drop.
Currently resonators are cooled with a liquid nitrogen bath and they are not directly supported from a cold finger with a spring, or supported with a spring from a cold radiation shield which is connected to the cold finger of a closed-cycle cryocooler.